stuff and stuff_copy are different lists, but the item at index 2 is a
list and they both point to the same list. This is true for all the
other operations we learnt: replication, concatenation and slicing.

The same principle extends to functions. Whenever we pass a variable
to a function as an argument, if it is a container, then the
variable is an alias to the list. We will go through this in more
detail in the function review.

Yes, there is a deepcopy function in a module called copy to resolve
this. For now, it is enough to be aware of this.